[Paper Review] Coexistence and Interference Mitigation for Wireless Body Area Networks: Improvements using On-Body Opportunistic Relaying

Jie Dong, David B. Smith|arXiv (Cornell University)|May 30, 2013

Wireless Body Area Networks12 references17 citations

TL;DR

This paper proposes on-body opportunistic relaying to enhance coexistence and mitigate interference in dense wireless body area networks (WBANs). Using TDMA and three-branch opportunistic relaying with fixed relays at the hips, it achieves up to 8 dB improvement in outage probability and significant reductions in level crossing rate, especially at low SINR thresholds, though average outage duration remains unchanged compared to single-hop systems.

ABSTRACT

Coexistence, and hence interference mitigation, across multiple wireless body area networks (WBANs) is an important problem as WBANs become more pervasive. Here, two-hop relay-assisted cooperative communications using opportunistic relaying (OR) is proposed for enhancement of coexistence for WBANs. Suitable time division multiple access (TDMA) schemes are employed for both intra-WBAN and inter-WBANs access protocols. To emulate actual conditions of WBAN use, extensive on-body and inter-body "everyday" channel measurements are employed. In addition, a realistic inter-WBAN channel model is simulated to investigate the effect of body shadowing and hub location on WBAN performance in enabling coexistence. When compared with single-link communications, it is found that opportunistic relaying can provide significant improvement, in terms of signal-to-interference+noise ratio (SINR), to outage probability and level crossing rate (LCR) into outages. However, average outage duration (AOD) is not affected. In addition a lognormal distribution shows a better fit to received SINR when the channel coherence time is small, and a Nakagami-m distribution is a more common fit when the channel is more stable. According to the estimated SINR distributions, theoretical outage probability, LCR and AOD are shown to match the empirical results well.

Motivation & Objective

• Address the challenge of coexistence and interference mitigation in dense WBAN deployments where multiple networks operate in close proximity.
• Investigate the performance gains of two-hop cooperative communications using opportunistic relaying in real-world on-body and inter-body channel conditions.
• Evaluate the effectiveness of fixed relay placement (left and right hips) versus dynamic relay selection in improving SINR-based reliability metrics.
• Derive theoretical outage probability, level crossing rate (LCR), and average outage duration (AOD) based on empirical SINR distributions.
• Identify the best-fitting statistical distribution (lognormal or Nakagami-m) for SINR under varying channel coherence times to support accurate performance modeling.

Proposed method

• Employs extensive on-body and inter-body channel measurements from real subjects to model intra-WBAN and inter-WBAN link gains.
• Uses time division multiple access (TDMA) for both intra-WBAN and inter-WBAN access, ensuring coordinated transmission scheduling.
• Applies three-branch opportunistic relaying (OR) where the best relay among three candidates forwards the packet per hop, minimizing complexity and power use.
• Models inter-WBAN interference using empirical inter-body path loss, shadowing, and small-scale fading, with a focus on body shadowing effects.
• Applies maximum-likelihood (ML) estimation to determine the best-fit statistical distribution for received SINR: lognormal for fast-fading (low coherence time), Nakagami-m for slow-fading (high coherence time).
• Derives theoretical first- and second-order statistics (outage probability, LCR, AOD) from estimated SINR distributions and validates them against empirical data.

Experimental results

Research questions

• RQ1 To what extent does opportunistic relaying improve SINR-based reliability metrics such as outage probability and level crossing rate in coexisting WBANs?
• RQ2 How does the placement of fixed relays (e.g., at left and right hips) affect interference mitigation and coexistence performance compared to single-hop transmission?
• RQ3 What statistical distribution best describes the SINR in WBANs under varying channel coherence times—lognormal or Nakagami-m?
• RQ4 Does cooperative relaying reduce average outage duration (AOD), a key metric for real-time WBAN applications?
• RQ5 How does body shadowing influence inter-WBAN interference and the effectiveness of cooperative relaying in practical scenarios?

Key findings

• Opportunistic relaying reduces outage probability by up to 8 dB at a 1% outage probability threshold compared to single-hop transmission, with consistent gains regardless of hub location.
• For Subject 1 (less stable channel), the scheme improves the SINR threshold by 4 dB at 1 Hz LCR and 7.5 dB at 0.1 Hz LCR, indicating strong interference mitigation at low SINR levels.
• For Subject 2 (more stable channel), improvements of 2.5 dB and 3 dB are observed at 1 Hz and 0.1 Hz LCR, respectively, demonstrating robustness across channel conditions.
• The lognormal distribution provides the best fit for SINR when channel coherence time is small (fast fading), while Nakagami-m distribution fits better when the channel is highly stable (large coherence time).
• Theoretical outage probability, LCR, and AOD derived from estimated SINR distributions match empirical results closely, validating the analytical model.
• Average outage duration (AOD) remains unchanged between single-hop and cooperative schemes, indicating no performance gain in this metric despite improvements in other statistics.